By the way, your plastic rep is over rating the durrability of MR-10. It is scratch resistant but not equal to glass. That being said, I have found that the MR-10 will hold up as well as the paint when brushing by things like evergreen trees. I prefer lexan over glass for reasons like breakage and less weight and I can rout it to shape myself.
Here http://www.tractorbynet.com/forums/build-yourself/140286-jd-4310-cab.html is my cab project.